Riffled pneumatic concentrating-table for gravitational separation of comminuted material



C. W. ECCLESTON. RIFFLED PNEUMATIC vCONCENTRATING TABLE FOR GHAVITATIONAL SEPARATION OF I COMMINUTED MATERIA.

m. QL 1T 5.,m 1 es mm JW d2 m m D.. R.. W 4... 2 E N .w D w... N O .H M 2 m fv P A CHARLES W. ECCLESTON, OF LOS ANGELES, CALIFORNIA.

RIFFLED PNEUMATIC CONCENTRATING-TABLE FOR GEAVITATINAL SEPABATION OF COMIVIINUTED MATERIA.

Application fi1ed J'une 24,

To all 'LU/Lont it 'may conccrn:

Be it known that I, CHARLES lV. Eocnns- Ton, a citizen of the United States, residing at Los Angeles, in the county of Los Angeles and State of California, have invented a new and useful Riffled Pneumatic Coneentrating-Table, for Gravitational Separation of Commi'nuted Material, of which` the following;` is a specification.

This invention relates to a transvei'sely inclined concentratin` table having a differential reciprocatin` motion which carries the comininuted material longitudinally forward toward the concentrates end of the table. Said table is adapted for the treatment of masses of comminuted materials containing particles of substances differing in specific gravity, which causes them to separato while more or less supported and buffeted by air expanded underneath the mass while the mass is in air of predetermined pressure such as atmospheric pressure, and subjected to impulses longitudinally of the table and to gravitational forces; and by means of which impulses the heavier particles are impelled along` the table with greater \"elocity than the lighter particles, so that the heavier materials beino' less susceptible to the buffeting impulses and being driven by the longitudinal impulses will out-travel the lighter material in one direction, while the lighter materials, being` more subject to thev bufeting impulses, and not being` subject to such rapid longitudinal travel, flow laterally upon the bulieting;` :surface formed at the pressure drop zone, and responsive to gravitational forccs, down the table slope and off of the table at the tailings discharge side thereof.

Tables of the general Character above refei'red to are well known, and the permeable element through which the air is introduced to the under side of the ilowing` mass of comminuted material to be gravitationally separated, classified or concentrated, has heretofore been subject to conditions which make the operation of such machines for any length of time very iiiconvenient and expensive. Heretofore in machines of this Character the permeable elements through which the air is forced beneath the mass of materials to be separated according' to specific gravities has been some form of fabric, or else a metal Speefication of Letters Patent.

Patented Julie 15, 1920..

1918. Serial NO. 241,707.

sheet slitted or punehed with numerous holes; but all such concentrating tables have been subject either to clogging with dust, or to excessive blast-like action of the air, depending on whether the material is canvas of hard spun filament, or a. very fine Wire cloth or some other material, constituting a permeable sheet in whichv the perforations are of Constant dimensions. In all former .machines of this class the Volume of air passing therethrough is dependent upon Constant oriiicial dimensions and the effect of increasing),` air pressures is to discharge the air withisome Velocity, as jets through numerous small nozzles. So far as I am aware, no pneumatic mineral concentrator using a fabric as its permeable table top has ever beenproduced, which is not subject to frequent clogging of the air delivery element; and this has been great source of loss and of expense in the operation of this class of machines; for the clogging, which occurs inevitably therewith, necessitates frequently stopping the work and removal and renewal of the separating Sheet; or replacement With new. The finer and more delicate separations cannot be effected with the slitted sheet metal top, and such material is only employed for the coarser classifications and separations.

I have discovered that all the inconveniences, ti'oubles. delays and expenses above referred to with respect to pneumatic yseparators or concentrators for fine work are 'caused by the use, as aforesaid, of fabric in the construction of the table top or permeable element, because of the permanent and fixed Character of the orifices through which the upwardly dii'ected air flow occnrs.

l have also discovered that the remedy is simple and cheap and easily applied, so that at a low cost any of the machines in which these troubles have been constantly present and well known for years, may be quickly transformed into machines to which all such troubles are foreign and in which they will never more occur.

An object of this invention is to provide a pneumatic Separator free from all liability to the great loss above referred to, and adapted for Constant operation day and night for an indefinite period ofl time without variations in the cliai'acter, quality and quantity of concentrates and tailings produced from a determined comminuted product to be separated according to gravities.

The principle of the invention and discovery is the discarding of the fabric and the slitted sheet metal forms of permeable concentrator table top and the replacing them with a permeable stretchable rubber sheet of delinite Character as will more fully hereinafter appear. i

The invention is broadly new and pioneer in this particular. That is to say, I have discovered there is an easy solution for the diificulties heretofore encountered and for the great expense now common to all socalled dry or pneumatic concentrators, and that the remedy resides in the construction of an apparatus with a permeable top made of a resilient, stretchable thin rubber sheet, punctured with numerous fine normally closed slit-like punctures, so as to allow the air to expand the punctures into perforations during the operation of the machine, and to cause the perforations to completely close after such air imposcd expansion has ceased; and the invention is regarded as broadly new and pioneer in this respect.

An object of the invention is to make provision for more gently diffusing the expanding upwardly directed compressed air throughout the mass of comminuted material at predetermined zones of pressure drop, so that the particles will all receive about the same application of buoying force at any particular zone under a certain pressure drop, thus allowing the differential motion and the table inclinations to operate uniformly on all particles of the same specific gra-vity throughout the respective zones and causing` the separations to be effected rapidly with the highest precision.

This invention marks a broadly new, primary and pioneer departure from former dry concentrating practice in that the air which is delivered to the underside of the comminuted mass in which the separation is to be effected, is delivered through openings varying in size and direction according to the conditions of operation; such as the relations of the weight of the comminuted body to the eXpansive lforce of the pneumatic pressure by which the air is applied to such body with varying pressure drop at various zones; and involves also an automatic adj ustment to the atmospheric pressures of varying altitudes; and, in fact, the operation of the machine involves a new method of concentration which consists in transmitting differential motion and applying pneumatic pressure to the underside of a comminuted mass by means of a thin stretchable india rubber sheet through orifices that are open only during` a stretching of the sheet respcnsive to the pneumatic pressure and varying in pressure drops at various zones and that are subj ect to increase and decrease in direct relation to the pneumatic and atmospheric pressures and to the weight of that portion of the comrninuted mass which is directly above the orifice through which the air issues to support said mass.

Another object is rapid and perfect separation of all the values from the gangue.

An object of the invention is to provide a pneumatic ore concentrator table in which the air from the air chamber will not pass through the table top until the pressure underneath the table top is equalized throughout so that the upward fiow of air at any structure point of the table will correspond to that at any other point of like structure irrespectve of the location of the air supplying pipe.

Another object is to subject lthe comminuted material; to various pressure drop zones and to various applications of the gravitational and pneumatic forces at each period of travel from riiile to riffle so that the particles in the material will be thoroughly buffeted and shaken apart in their progress from zone to zone over the table top, thus to facilitate the separation according to specific gravities.

Other objects and advantages may appear from the accompanying drawings, the subjoined detail description and the appended claims.

The invention may be carried out in various forms and the accompanying drawings illustrate the invention in a form I at present deem most desirable.

Figure 1 is a diagrammatic end elevation of a riffled dry concentrator constructed in accordance with this invention.

Fig. 2 is an enlarged fragmental crosssectional elevation of the riffled dry concentrator table shown in Fig. 1 out of action. Line x2, Fig. 8, indicates the plane of section.

Fig. 3 is a fragmental elevation of the concentrator table top in section on line 'm3, Fig. '7; three riffles and fragments Vof their supports being shown. The thickness of the punctured sheet is exaggerated and perforations shown as being viewed at right angles to their length. A mass of comminuted Inaterial is shown in a state of partial separation as it may appear during the operation.

Fig. a is a fragmental view of the sheet in section on line m4, Figs. 3 and 7 viewing` the perforations from a sectional plane parallel to the riflies and oblique to the sides of the slits.

Fig. 5 is a full-size detached fragmental view of the normally unstretched dry-concentrator table top sheet or permeable medium shown in Figs. 2, 3 and 4; the width of the punctures beingexaggerated.

Fig. 6 is an enlarged fragmental plan of the surface sheet or permeable medium out of action as shown in F ig. 2. The slit-like punctures are shown proportionally enlarged in both width and length.

Fig. 7 is a fragmental plan on the scale of Fig. 5 showing the top face of the permeable medium as the same may appear when stretched in action.

Fig. 8 is a broken fragmental plan in reduced scale, of the table shown in Fig. 1.,

' superposed on the Sheet and clamp the Sheet to the bars. Said sheet and riifle-supporting wind brake bars are carried by the table frame in which is formed the air pressure Chamber (3, the bottom of which chamber is formed by a metal sheet 7 through which air is admitted to said chamber by pipe 8, and which during operation is impermeable to the air pressure produced through such pipe.

The riflied pnenmatic concentrator table thus formed is supported by the shaking frame 9 supported by Springs 10 and operated by a differential motion device 11 of any of the well-known forms commonly used for giving differential reciprocating motion to Separating tables.

The numerous small punctures 2 are normally closed by the elasticity of the rubber Sheet and are opened by action of the pneumatic pressure during the operation of the concentrator.

The top surfaces of the riflies of the' table thus constructed lie about or exactly in a common plane that, in practice. may be adjusted as to slant by any well-known means, not shown; and provision is made for the free flow of comminuted material over said surface.` and free dischargeof tailings over said riffles in one direction. and free discharge of values in another direction along the channels 12 between the riffles. The speed with which the discharge of tailings and values oce'nrs will depend upon the slope adjustment of'the table as is wellknown in the art.

in tables of the Character referred to, the material to be treated is fed to the surface of the table top by any suitable means, not

shown7 and. said surface is in air of lower pressure than that of the compressed air Chamber; so that the compressed air which opens the punctures and flows out through the Sheet7 buoys up the material in the air of predetermined lower pressure to which the compressed air flows.

In practical operation when air is compressed into the compressed air chamber 6, it stretches and bows the india rubber Sheet upward, thus forining a ridge 12 along the spaces between the rifiies and opening the slits on the upper side to a greater eXtent than below; and thus the expanding air is given a diffusing direction away from the mid-line of the elit-like openings and the tendency of impelling` the air as from a multitude of nozzles is avoided. The air streams are also modified by their contact, under pressure, with the soft rubber walls of the slits; thus tending to set up along the mid-lines of the slits, respectively, laterally expanding currents that frictionally act upon the air that is in frictional contact with the soft rubber walls of the slits; the result being a tendency to more immediately spread the escaping air over the interslit spaces and thereby making a practically uniform sustaining and constantly upwardly moving and upwardly and laterally expanding air body at each particular zone above the table.

By arranging slits in rows side by side at close intervals and spacing the rows a greater distance apart, the expansion of the air endwise of the slits bridges the space between the rows with compressed air of somewhat less expansive force than that of the expanding air directly above the rows of slits; so that as the comminuted material flows over the surface, it is subject to gentle successive rising and falling action caused by the differences in upward pressures; this action, tending to assist in the separation of the partioles by an undulating or riiiled buffeting action on the stream of flowing material that is carried alonir commingled with the compressed and expanding air medium that supports the comminuted above the top of the table.

The rows of punctures are arranged in parallelism at regular intervals apart; and the spaces between the rifiies are preferably multiples of the spaces from center to center of the rows of punctures so that a row of punctures will lie close to the approach side of each rifiie.

The sheet forming the top of the table is clamped to the shaking frame 9. and the Springs 10 which support said frame are carried by posts 13. The differential motion is applied to the table by any differential motion device well known in the arts connected to loop 1d opposite to the concentrates end 14' of the table. The air is supplied by pipe 8 from any suitable source such as the cycloidal blower 15 connected to thepipe by a flexible hose 16. which is Slack to permit reciprocating motion of the table.

The riflles 4 are of gradually reduced depth from the head of the table toward the concentrates end thereof as shown in Fig. 9.

The stretchable linely punctured sheet 1 is preferably of india rubber, thus securing an impervious Character capable of holding iiuids such as air and water, eXcept when the sheet is stretched, and also possessing great elasticity and durability under the conditions imposed by the work.

The normally closed punctures 2 may be produced in various ways, and in the rubber sheets I have used, 1 have produced the punctures by means of a pointed needle 17, having a triangular cross-section with sharp corners and working through a thrust plate 18 having a hole 19 that its the needle at the thickest portion thereof which passes through the sheet. Said needle may be operated by means of an ordinary sewing machine mechanism not shown, fitted with said plate; parallel lines of punctures being made by running the sheet through the sewing machine in the same manner as though the sheet were being stitched by the machine. These punctures may be made as large or small as deemed advisable, and the rows as close together as desired; and 1 have employed punctures consisting of slits each of which is about 33g of an inch in length extending through a sheet somewhat less than 31g of an inch in thickness. These proportions or others may be employed as found advisable. The triangular needle suitable for making holes of the character stated is 3333- inch across the face at the largest cutting part.

It is deemed preferable to make the punctures in the form of slits so that ,as the material is stretched, the punctures will be eX- panded according to the angle of the sheet and the amount of stretch to form openings therethrough that are very narrow and fine, but capable of allowing considerable air under pressure to fiow through.

ll find that the needle above describcd does not form a three-cornered hole in the rubber, but makes a slit that opens and closes as the eXpansion and contraction occurs.

lt is understood that the sheet may be of any suitable thickness and that various lengths of slits may be made in such material, the principle being` that the material shall be of such character that when the sheet is normal7 that is to say, not stretched, the slits will be closed and the sheet will be impervious to the passing of fiuids and other highly mobile materials under a limited pressure which may be predetermined for the different concentrator tables.

l have operated the table lto good advantage with a pressure of from one to four pounds pressure per square inch with J; to inch Vdepth of pulp, but do not limit'the operation to such pressures or depths.

in action, the mass of comminuted material flows freely over the tops of the riliies A as though subject only to the action of the differential motion and the force of gravity. The air enlivens the pu'lp so that it is highly fiuid. It is noted that there are several zones of operation as a, Z), c, cl, e, f, g; and that the comminuted material in the respective zones is difi'erently acted upon by the forces at work. At the zone a the comminuted material fiows over the top of the riflie and is subject only to the forces of gravity,

to friction of the riffle, and to the differential motion.

As the pulp passes from the rifiie into zone b it falls directly by gravity and is less subject to the force of the differential motion. At the onward side of the zone Z) and throughout the zones o, d, e and f the mass is subject to the enlivening action of the expanding air that issues from the perforations 2 which have been opened up by the expansive force of the air from the Chamber 6. The air from the perforations in zone o is directed upward aslant toward the downwardly onfiowing material of zone Z): As such material passes the perforations 2 in zone d, the air fiows more directly upward and in the direction reverse to that of the force of gravity. As the material passes over the perforations in zone the enlivened mass is subject to the air pressure from the perforations 2 of said zone e, and in zone f the air is directed with the onfiowing current of comminuted material, thus tending to lift it toward the top of the next rifHe. In the zone g the heavier material at the base of the riffie is brought to a standstill so far as the lateral onward movement is con- 'cerned and the lighter material is caused to ascend; this operation being` hastened by the' air from the perforations in zone g which air is directed up along the upper wall formed by the upper edge of the riflle. The

efi'ected. As the heavier material increases in depth, and is moved longitudinally along the rear side of any riflle7 the heavy values deposit on the rubber sheet, the pulp being enlivened by vertically directed air flowing up from the perforations that are close to the upper or approach side of the rifiie. On each cross section the onward flow is substantially such as shown; the overflow of the 10 lighter comminuted material occurring, however, at a lower level and this is repeated from riflle to rifile, there being a succession of zones a, Z), c, cl, e, f and g for each space between the approach sides of any two succeeding riflies from end to end thereof; the depth of light material gradually decreasing and that of heavy material gradually increasing tothe discharge end of the riffles. In this way a continuous skimming process goes on at each riffle and each ridge, and very fine separations may be made between materials of different specific gravities. Such separations are made rapidly and the flow of comminuted material over the riffies where inch high may be a half inch in depth, without loss of values, the flow being very rapid and continuous from the higher edge to the tailings discharge edge of the table, and the flow of the concentrates toward the concentrates end of the table being facilitated by the ridges formed by the sheet when bent up by the air.

The lighter material commingled with the expanding air, moves transversely of the table as freely as water but the delivery of the air thereto is effected so evenly that it does not raise dust. Although the air is given different directions by the perforations in the different zones, the air expands and becomes diffused throughout the mass before it reaches the top surface of the pulp.

The air pressure bows the rubber sheet up between the riffies and thus opens the punctures more or less according to the angles and the expansion and gives various directions to the air jets that issue therethrough; as will be understood from Figs. 3 and l, with the result that the particles of comminuted material are shaken and tossed about and a complete separation is eifected without allowing any jet like escapes of air to occur; but the comparatively broad bars 3 extend beyond the onward face of the riffle so as to form a wind shield 20 thus affording a practically dead air space in zone Z), through which the pulp may fall from the top of the riffle. The approach sides of the bar and riffle are flush with each other.

For convenience of description the side h' of the riffle at which the pulp first arrives as it fiows across the table top, is termed the approach side of the riiile; and that side z' of the riflie over which the pulp falls in passing onward from the riflie is termed the onward side of the ritlle and so far as I am aware I am the first to provide a cocentrator table top constructed to form the successive zones above described, between the approach sides of two succeeding rifiles.

By reference to Fig. 9 it will be understood that the longitudinal traces y' of the table surface between and parallel to any two successive rifiies are straight and practically level and that the tops of the rifi'les slope down to such surface in a manner customary to the riifles of former concentrator tables, and that the low ridge 12 extends to a practically uniform level between the riifles from end to end thereof, being lower than the riffie tops at the head of the table, and higher than the riifles at the concentrates discharge end of the table so that the particles which are heavy enough to lodge before the ridge will pass on to the concentrates end of table and will pass off without increasing the depth of the string of concentrates intercepted by the succeeding riflie.

In my application for Letters Patent of the United States, filed August 23, 1916, Serial No. 116,555, I have shown a mineral Separator comprising a table, a top therefor formed of a rubber sheet having slot like needle perforations therethrough that are normally closed and that are adapted to be opened by air pressure; means whereby air pressure is applied therethrough from below to comminuted material to separate the gangue from the values, and means for delivering comininuted material to the table top; and no claim is made herein to the subject matter' just stated for the reason that the same is broadly claimed in said prior application. The presentapplication is to specific construction and arrangements set forth in the claims appended hereto.

I claim2- 1. A pneumatic concentrating table comprising a rubber sheet having therethrough numerous punctures normally closed by the elasticity of the sheet; said sheet being eX- posed on its underside to pressure of air and having its upper side open to and in direct contact with air of lower pressure so that coinminuted material passing over the sheet in the air of the lower pressure will be directly subject to the said air of lower pressure and so action of the compressed and expanding air issuing through perforations formed by the opening of the punctures caused by the passage of the compressed air therethrough will buoy up the lighter material; and riflies on the surface of the rubber sheet to catch the heavier material.

2. A concentrating table top comprising a sheet of elastic stretchable material having fine punctures normally closed therethrough, in combination with rifiles on top of such sheet, said riffles and said top of the sheet being in air of lower pressure, means to Supply compressed air to the under-side of the Sheet to stretch the same upward into said air of lower pressure and to open said punctures to said upper air of. lower pressure so that material in air of lower pressure may be subjected to a gravitational action according to the differences of pressure involved.

3. A dry ore concentrator table comprising a frame7 a stretchable rubber Sheet fastened to the frame and provided with punctures that are normally closed; bars arranged at intervals apart below such sheet to support it and to intercept the passage throughout of compressed air at intervals; riflie Strips arranged on the Sheet along above the bars and clamping the sheet on the bars in normal flat and unstretched condition; the riflie strips and top of the sheet being subject to air of lower pressure; means to apply air. pressure to the under side of the sheet to belly the same upwardly thus to open the punctures and supply a variable air pressure to the spaces between said riffles, and means to apply differential motion to the tables.

4. 111 combination with a transversely inclinedv concentrating table frame having a differential reciprocating motion which carries the material longitudinally forward toward the concentrates end of the table; a rubber Sheet forming the top of the table, and rifiles decreasing in depth toward the concentrates discharge end, fastened upon said Sheet; said Sheet being punctured between the riffles with slits that are adapted to be expanded into perforations when the Sheet is stretched upward; and means to apply air pressure to Stretch the Sheet and to cause a fiow of air through the perforations, and a flow of comminuted material over the rifiles as the top is reciprocated.

5. A pneumatic concentrating table comprising a-rubber Sheet having therethrough numerous punctures arrangedf in parallel rows and normally closed by the elasticity of the sheet said Sheet being exposed on its underside to pressure of air and having its upper side open to air of lower pressure so that comminuted material passing over the sheet in the air of the lower pressure will be directly subject to the action of the compressed and expanding air issuing through perforations formed by the opening of the punctures caused by the passage of the air therethrough; riffles extending in parallelism with the rows; there being a plurality of rows of punctures between the yriffles; the rubber Sheet being adapted to bow upward in ridges respectively between the riflles whereby varying passages for the compressed air are opened up below the riffies; and means to give differential motion to the table longitudinally of the riffies.

6. A. concentrating table top comprising near-3,497

a Sheet of elastic stretchable material having filie punctures normally closed therethrough, in combination with rifiies on top of such Sheet, means to supply compressed air to the under-Side of the Sheet to Stretch the same upward into air of lower pressure and to open said punctures to said upper air of lower pressure according` to the differences of pressure involved and according to the various angles and expansions of the sheet; said table top being aslant transversely of the rifiies and means to apply differential motion to Said table top.

7. A dry ore concentrator table comprising a frame, a stretchable rubber sheet fastened to the frame and provided with punctures that are normally closed; bars ai'- ranged at intervals apart below such Sheet to support it and to intercept the air at intervals; riflle Strips arranged on the Sheet along above the bars and clamping the sheet on the bars in normal fiat and unstretched condition; said. bars forming wind brakes at the onward side of the table; means to apply air pressure to the under side of the sheet to belly the same upwardly thus to open the punctures and supply a variable air pressure to the spaces between said riffies according to the various angles and expansions of the sheet, and means to apply diferential motion to the tables.

8. A concentrator table having a riffied top and provided between the rifiies with punctures through which air under pressure may be forced; said top being provided, while in action with longitudinal ridges between the riflies; said ridges being lower than the riffles and provided with said' punctures.

9. A concentrator table having a riffied top and provided between the riffies with a surface having punctures through which air under pressure may be forced; said top being provided, while in action with longitudinal ridges between the riffies; said ridges being lower than the rifiles and provided with said punctures; and wind brakes at the onward sides of said riffies to allow the comminuted material to fall to said surface as it passes over the riifle.

10. A dry concentrator table for gravitational separation of comminuted material7 comprising an air pressure chamber having a permeable top formed with bars, a thin rubber sheet, and rifiies, which riflies and upper face of the thin rnbber sheet are subjected to a predetermined air pressure; said sheet having slits therethrough and applied to the upper side of said bars; and the rifi'les being on the Sheet directly over the bars and being formed of strips reduced in depth from the head of the table toward the concentrates end of'the table and' being fixed to the top of the sheet; said A'u'ubber Sheet being punctured with slits that are normally closed to resist initial pressure of air within the Chamber and adapted to open into air of predetermined pressure under additional pressure within the chamber When such additional pressure becomes great enough to bend and stretch the rubber upward at intervals underneath the load of comminuted material on the table.

11. A dry concentrator table adapted for gravitational Separation of comminuted material, comprising an air pressure Chamber having a permeable laterally inclined top formed with bars, a thin rubber Sheet and riflies; the thin rubber Sheet having Slits therethrough and being applied to the upper Side of said bars; and the rifiies being formed of Strips reduced in depth from the head of the table toward the concentrates end of the table; the riflles and top surface of the Sheet being subject to a predetermined air pressure; the longitudinal traces of Said table being level and the tops of the ri'lfles Slanting down toward the table top from head to eoncentrates charge; said rubber Sheet being punctured with slits that are normally closed to resist initial pressure of air within the Chamber and adapted to open under additional pressure when such pressure becomeS great enough to bend and stretch the rubber upward underneath the load of comminuted material on the table; means to supply comminuted material to the head of the table, and means to supply air pressure' to the underside of the rubber Sheet.

12. A pneumatic concentrator table top comprising Supporting bars and rifiles Superposed thereon and a thin Stretchable rubber Sheet clamped between said bars and riffles; said Sheet being provided with punctureS that are adapted'to form slits to allow compressed air to pass therethrough when the Sheet is Stretched by air pressure from below; said slits being arranged in rows that extend parallel to the Sides of the riflies and also being arranged with their longer axes oblique to the aXiS of the row and to the Side of the rifiles.

13. A pneumatic concentrator table top comprising supporting bars and rifiies superposed thereon and a thin Stretchable rubber Sheet clamped between said bars and riffles; Said. Sheet being provided with punctures that are adapted to form slits to allow compressed air to pass therethrough when the Sheet is stretched by air pressure from below; Said 'slits being arranged in roWS that extend parallel to the sideS of the riffies and also being arranged with their'longer axes oblique to the aXiS of the row and to the side of the rifiies; the spaces between the rows being of greater width than the spaces between the slits of a row.

lll. A pneumatic ooncentrator table top for gravitational separation of comminuted material, comprising a punctured stretchable rubber Sheet; Supports therefor and riffies on top of the Sheet above the supports, the Sheet and rifles above the sheets being subjected to a predetermined air pressure; there being punctures in the Sheet between the riflles adapted to allow air under pressure to flow up through rubber to buifet the comminuted material according to the stretching of the rubber by compressed air from below.

15. A pneumatic concentrator table top constructed of a punctured stretchable Sheet and riflles arranged to form zones where the pulp is Subjected to varied Operations of forces in succession in the order named; that is to say, frictional zone for action of a riffle, practically unobstructed gravitational deScent from the riffle top; action of expanding air directed toward the onward Side of the falling pulp; a zone for retardation of onward fiow of pulp, said zone being formed by a gentle ascent of the Sheet; means to cause expansion of upwardly directed expanding compressed air; means to cause expansion of compressed air direoted with the onward flow of the pulp; means to cause a banking of the pulp against the approach Side of a rifiie; and means to cause the expansion of compressed air directed upwardly at the approach Side of the rifle.

16. In a dry concentrator of the class Specified; a permeable and stretchable Sheet rubber table top Surface and riffles along the surface; there being a low ridge between each two Successive rifiles subject to VariationS of pitch as the relative air pressures vary.

17. In a dry concentrator of the class Specified; a permeable table top Surface and riffles along the surface; there being a low ridge between each two successive riffles, the permeable surface having perforations that in action direct air toward the pulp approaching the ridge on one side and with the flow of pulp on the onward Side of the ridge.

In testimony whereof I have hereunto Set my hand at Los Angeles, California, this lizth day of June, 1918.

CHARLES 7W. 'ECCLESTON Witness:

J AMES R. TowNsEND. 

